Performance of channel estimation determines the performance of a signal demodulator. Current Digital Terrestrial Multimedia Broadcast (DTMB) protocol defines three frame structures for channel estimation. Conventional channel estimation in DTMB system uses the auto-correlation property of pseudo-random noise code (PN) sequence in the frame header. However, due to 1) data interference caused by multipath channel, 2) non-ideal auto-correlation property of PN sequence in some frame structures, and/or 3) copied PN that may cause mirrored path in channel estimation when the length of channel estimation is longer than PN length, which may require different channel estimation methods for different time delay paths, the performance of conventional channel estimation method in DTMB system is undesirable. Therefore, it is desirable to design a demodulator that may be accurate and applicable to different frame structures.